206 



INDUCTION. 



if properly made, it would be conclu- 

 sive. Here, then, is a general law of 

 nature, inferred without hesitation 

 from a single instance ; an universal 

 proposition from a singular one. Now 

 mark another case, and contrast it 

 with this. Not all the instances 

 which have been observed since the 

 beginning of the world in support of 

 the general proposition that all crows 

 are black would be deemed a suffi- 

 cient presumption of the truth of the 

 proposition, to outweigh the testimony 

 of one unexceptionable witness who 

 should affirm that in some region of 

 the earth not fully explored he had 

 caught and examined a crow, and 

 had found it to be grey. 



Why is a single instance, in some 

 cases, sufficient for a complete induc- 

 tion, while in others myriads of con- 

 curring instances, without a single ex- 

 ception known or presumed, go such 

 a very little way towards establish- 

 ing an universal proposition? Who- 

 ever can answer this question knows 

 more of the philosophy of logic than 

 the wisest of the ancients, and has 

 solved the problem of Induction. 



CHAPTER IV. 



OF LAWS OP NATURE. 



§ I. In the contemplation of that 

 uniformity in the course of nature 

 which is assumed in every inference 

 from experience, one of the first ob- 

 servations that present themselves is, 

 that the uniformity in question is not 

 properly uniformity, but uniformities. 

 The general regularity results from 

 the co-existence of partial regularities. 

 The course of nature in general is 

 constant, because the course of each 

 of the various phenomena that com- 

 pose it is so. A certain fact invari- 

 ably occurs whenever certain circum- 

 stances are present, and does not 

 occur when they are absent ; the like 

 is true of another fact ; and so on. 

 From these separate threads of con- 

 nection between parts of the great 

 whole which we term nature a gene- 



ral tissue of connection unavoidably 

 weaves itself, by which the whole is 

 held together. If A is always ac- 

 companied by D, B by E, and C by 

 F, it follows that A B is accompanied 

 by D E, A C by D F, B C by E F, 

 and finally A B O by D E F ; and 

 thus the general character of regula- 

 rity is produced, which, along with 

 and in the midst of infinite diversity, 

 pervades all nature. 



The first point, therefore, to be 

 noted in regard to what is called the 

 uniformity of the course of nature 

 is, that it is itself a complex fact, 

 compounded of all the separate uni- 

 formities which exist in respect to 

 single phenomena. These various 

 uniformities, when ascertained by 

 what is regarded as a sufficient in- 

 duction, we call in common parlance, 

 Laws of Nature. Scientifically speak- 

 ing, that title is employed in a more 

 restricted sense to designate the uni- 

 formities when reduced to their most 

 simple expression. Thus in the illus- 

 tration already employed, there were 

 seven uniformities : all of which, if 

 considered sufficiently certain, would, 

 in the more lax application of the 

 term, be called laws of nature. But 

 of the seven, three alone are properly 

 distinct and independent : these being 

 pre-supposed, the others follow of 

 course. The three first, therefore, 

 according to the stricter acceptation, 

 are called laws of nature ; the re- 

 mainder not ; because they are in 

 truth mere cases of the three first : 

 virtually included in them ; said, 

 therefore, to result from them : who- 

 ever affirms those three has already 

 affirmed all the rest. 



To substitute real examples for sym- 

 bolical ones, the following are three uni- 

 formities, or call them laws of nature : 

 th e 1 aw that air has weight, the law that 

 pressure on a fluid is propagated equally 

 in all directions, and the law that pres- 

 sure in one direction, not opposed by 

 equal pressure in the contrary direction, 

 produces motion, which does not cease 

 until equilibrium is restored. From 

 these three unifonnities we should 



